Have a look at Tamil's blog post about this to see how to do it. You may have to read through some of the comments to see how to apply this to Opera 11 as the instructions were written a long time ago and many menu paths have changed. There are also some caveats with extensions not showing up by default, I believe.

Having said that, why on earth would you want to change the ordering? It makes much more sense to have separate address bars for each tab, you can even start typing something in one tab, check something on another tab, come back to the first and continue typing. Even Firefox has recognised that this way makes more sense and has changed the ordering to be the same as Opera. Chrome also uses this order. But, being Opera, you can customise the UI pretty much however you want...